When the Bio::Das->features() method is called with the -iterator argument, the method will return an iterator over the features returned from the various data sources. Each feature can be returned by calling next_seq() iteratively until the method returns undef.

This is not as neat as it seems, because it works by creating all the features in advance and storing them in memory. For true pipelined access to the features, call features() with a callback subroutine.